This invention relates to a blood pressure recorder, and more particularly, to a portable blood pressure recorder for an ambulatory subject. Blood pressure measurement is valuable in clinical medicine and experimental psychology, and is performed by direct and indirect methods. When systolic and diastolic pressures are sufficient, an indirect method is normally employed thereby avoiding the trauma and possibilities of infection associated with the direct method.
Nearly all indirect methods occlude the blood vessel through application of counterpressure on the body surface. Certain physiological events are detected as this counterpressure is varied. Systolic and diastolic pressures are equated to this counterpressure whenever specific changes in these physiological events occur.
The following references are generally representative of the present art:
U.S. Pats. PA1 Publication of Del Mar Avionics dated 12/77
Nakayama et al: No. 4,144,879 PA2 Matsuoka et al: No. 4,105,020 PA2 Kaspari et al: No. 4,058,117 PA2 Yen et al: No. 3,978,848 PA2 Lichowsky: No. 3,905,353 PA2 Lickowsky: No. 3,905,354 PA2 ("Ambulatory Pressurometer II System")
Available instruments for blood pressure determination are less than ideal for several reasons. Application is generally restricted to specific subject activities and locations, the subject normally being seated or recumbent, and in a fixed setting, such as a doctor's office or a nursing station. Most instruments are manually operated, requiring supervision and thereby limiting the amount of data which can be generated practically. Furthermore, many blood pressure instruments provide questionable measurements due to noise-related data reduction. Noise is typically detected at the same frequency and amplitude as the signal. Data reduction in the early stages of measurement reduces the capability of subsequently sorting out a signal from remaining noise. In addition, blood pressure may be significantly affected by the subject's emotional response to the process of blood pressure measurement. These restrictions are especially severe when the application involves numerous indirect measurements on ambulatory subjects.
The invention overcomes these limitations by providing a portable device which allows relatively unrestricted movement of the ambulatory subject, automatically measures blood pressure periodically throughout eight or more hours of a day, and stores this information for later retrieval and analysis. The invention utilizes the ausculatory method to measure blood pressure. A standard inflatable occluding cuff is wrapped around a subject's arm for measurement purposes. A microphone, taped securely at the antecubital fossa (brachial artery) and compressed by the arm cuff, detects Korotkoff sounds. When the device is activated, a pump pressurizes the cuff. Once a predetermined pressurized level is reached in the cuff, the pump is deactivated and measurement begins. The pressure in the cuff falls until a lower setting is reached. As the pressure decreases, data is collected in encoded, uniform pressure segments. The data is then recorded for subsequent analysis.